Wearable Garment vs Gel Electrodes for Electrical Muscle Stimulation

A Crossover Randomized Controlled Trial Comparing Smart Textile and Hydrogel Electrodes for Neurostimulation in Healthy Adults

The goal of this study is to evaluate whether textile-based electrodes can provide neurostimulation that is comparable in comfort and effectiveness to traditional hydrogel electrodes in healthy adults.

The main questions it aims to answer are:

1. Is the perceived sensation of stimulation using textile electrodes non-inferior to that of hydrogel electrodes?
2. Is the current required to evoke muscle contractions similar between textile and hydrogel electrodes?

Each participant will complete three stimulation conditions in random order across separate visits:

1. hydrogel electrodes (standard),
2. dry polymer-textile electrodes with lotion, and
3. dry textile electrodes with hydrogel pads

Electrical stimulation will be delivered to the lower leg muscles using a wearable sleeve with integrated electrodes. The investigators will assess sensorimotor thresholds (e.g., detection, motor, and full motor threshold), skin-electrode impedance, and torque. Participants will also rate stimulation comfort, intensity, and sensation location via questionnaire.

After the three primary arms, participants may optionally complete two additional arms using different moisturizers applied to the textile electrodes to evaluate their impact on stimulation performance.

The results of this study will help determine whether textile electrodes can be used as an effective and comfortable alternative to hydrogel electrodes in wearable neurostimulation applications.

Neurostimulation involves the use of electric current delivered through skin-surface electrodes to activate muscles. It is commonly used for purposes such as muscle strengthening, motor function improvement, blood flow enhancement, and in neuroprostheses. Standard neurostimulation systems typically rely on disposable hydrogel electrodes, which can cause skin irritation and tend to dry out over time. These limitations make hydrogel electrodes less suitable for long-term or repeated use.

Textile-based electrodes are an emerging alternative. These electrodes are integrated into wearable garments, making them washable, reusable, and more comfortable for extended wear times. However, research directly comparing their effectiveness and user experience compared to hydrogel electrodes is limited.

The goal of this study is to compare textile electrodes to gold-standard hydrogel electrodes for muscle activation and perceived stimulation sensation. The investigators hypothesize that: 1) there will be no clinically meaningful difference in participants' perception of the stimulation between textile and hydrogel electrodes, and 2) there will be no significant difference in the stimulation current required to elicit functional contractions.

This is a crossover randomized controlled trial involving three primary arms: 1) hydrogel electrodes, 2) dry polymer-textile electrodes with lotion, and 3) dry textile electrodes with gel pads applied. Each participant will perform all three arms in a randomized order with at least 24 hours between visits. Stimulation will be delivered to the calf and tibialis anterior muscles using the same electrical stimulator and settings in all conditions. Following completion of the three primary arms, participants will be given the option to complete an additional two arms using different types of commercially available moisturizers on the dry textile electrodes to assess comparative on-body performance of different water-based moisturizers. All moisturizers are commercially available and are labelled Skin Lotion A, B, and C in the 'Arms and Interventions' section.

A sample size of 18 participants is required to detect a Cohen's f of 0.40 with 95% power and a significance level of ⍺ = 0.05 for a within-subjects one-way repeated measures analysis of variance (ANOVA) with three conditions. To preserve statistical power, the investigators will recruit 20 participants. Pilot data comparing textile to hydrogel electrodes provided an estimated effect size of f = 0.65. Given the pilot data was not randomized, which likely inflated the observed effect size, the investigators conservatively based their sample size calculation on a Cohen's f of 0.40 (i.e., a large effect size) to ensure adequate power to detect a potentially smaller true effect.

A non-inferiority analysis will compare perceived stimulation intensity on a 10-point numerical rating scale. A 2-point difference is set as the non-inferiority margin based on prior research on the minimal clinically important difference. Textile electrodes will be considered non-inferior if the upper bound of the 95% confidence interval for the difference in intensity remains below this threshold. Repeated measures ANOVAs and Tukey's post hoc tests will be used to analyze the outcome variables where appropriate.

Inclusion Criteria:

• Healthy (without a known diagnosis of cardiovascular, pulmonary or neurological condition)

Exclusion Criteria:

• Known pregnancy
• Implanted defibrillator or pacemaker
• Pain in the body part being tested
• Open wound or dressing (e.g. band-aid) on a body part that needs to be in contact with the electrodes
• Severe frailty such that donning or doffing the garment may cause a danger of falling